Primer composition and bonded structure

ABSTRACT

There is provided a primer composition capable of effectively enhancing anti-plasticizer property and water resistance even without curing of the primer layer, and a bonded structure. A primer composition forms a primer layer, containing a polymer, of a paint film formed by painting and drying on a surface to be painted; and a bonded structure includes: a base material, a primer layer containing a polymer sticking fast to the base material, and an adhesive sheet having an adhesive layer stuck fast to the primer layer. The polymer contains a polycarbonate polyurethane having a repeated unit derived from polycarbonate polyol in a molecule thereof.

FIELD OF THE INVENTION

The present invention relates to a primer composition and a bondedstructure. More particularly, the present invention relates to a primercomposition that can increase plasticizer resistance and waterresistance of a primer layer without curing the primer layer to a bondedstructure.

BACKGROUND OF THE INVENTION

In a bonded structure consisting of a base material and an adhesivesheet to be bonded to the base material, a primer layer is oftenprovided between the base material and the adhesive sheet.

The primer layer is usually formed by coating a primer compositioncomprising a polymer (primer polymer). Two types of primer layers haveconventionally been used. One is a cured primer layer formed by curing acoated primer composition and the other is an uncured primer layer thatcan be obtained by simply coating and drying a primer composition.

For example, the cured primer layer is disclosed in Japanese PatentApplication Laid-open No. 7-52305. The Patent Application discloses anexterior decorative material for buildings, which is a bonded structureformed from a base material made from a mixture of an inorganic material(e.g., a calcium silicate material) and a fibrous material, a primerlayer containing a cured resin formed on the surface of the basematerial, and a decorative sheet adhered to the surface of the primerlayer. Typically, the decorative sheet has an adhesive layer thatadheres to an exterior member via the adhesive layer. The cured resin isformed from a curable resin. Examples of curable resins that form thecured resin include an epoxy resin, polyisocyanate resin, urethaneresin, and acrylic resin.

Such a cured primer layer is advantageous for increasing weatherresistance, water resistance, plasticizer resistance, and the like.“Plasticizer resistance” means a plasticizer contained in a basematerial is prevented from moving to the adhesive layer of an adhesivesheet. If the plasticizer moves to the adhesive layer, the cohesiveforce of the adhesive layer is impaired. A decrease in the cohesiveforce induces a decrease in the adhesive force of the adhesive sheetwith the base material (the primer layer) and may cause the adhesivesheet to release from the bonded structure during use. As an example, abase material has an outermost layer consisting of a plasticized resinlayer that contains a resin and a plasticizer for the resin. Such a basematerial is used as an interior decorative board. The adhesive sheet(e.g. a decorative sheet) is used for repairing the interior decorativeboard, remodeling the inside and outside walls of buildings formed fromthe interior decorative board, and the like by adhering to the surfaceof the interior decorative board.

On the other hand, the uncured primer layer is disclosed in JapanesePatent Application Laid-open No. 2001-199195. The primer compositiondisclosed in the Patent Application contains an acrylic resin (acore-shell type acrylic emulsion resin) as a primer polymer.

In the cured primer, after applying the primer composition containing acurable resin to the surface of a base material, the primer layer mustbe aged for curing. A comparatively long time is required for completingthe aging of the primer layer. In addition, in the case of a two-liquidtype primer composition consisting of a main agent liquid and a curingagent liquid, these two liquids must be weighed and blended in aprescribed proportion at the production site. A one-liquid cured primercomposition (moisture cured, for example) can be processed more simplythan the two-liquid type. However, this type of primer is inconvenientdue to difficulty in storing for a long period of time.

Some primer layers may be used without curing such as in the case whenan acrylic resin is used (described above). However, such acrylic resinprimer layer exhibits comparatively high affinity to plasticizers.Therefore, it is difficult to prevent a plasticizer from moving from thebase material to the adhesive layer of an adhesive sheet when an acrylicprimer is used without curing.

Alternatively, it is possible to use polyurethane as a primer polymerwithout curing the primer layer. However, such a primer layer has othertypes of problems associated with such a primer layer. Specifically,since polyester polyurethane is a fairly common polyurethane and iseasily hydrolyzed, it is difficult to increase the water resistance. Adecrease in the water resistance induces a decrease in the adhesiveforce of the adhesive sheet with the base material (the primer layer)and may cause the adhesive sheet to release from the bonded structureduring use.

A primer layer formed from an aqueous primer containing a primer polymerdispersed in an aqueous medium particularly tends to decrease the waterresistance. Increased water resistance is required for adhesive sheetsused as an internal decorative sheet on the walls or floors of roomswhere water is used such as a bathroom, kitchen, lavatory, and indoorpool.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above problems inconventional technologies. Briefly, in one aspect, the present inventionprovides a primer composition and bonded structure that can produce aprimer layer on the coated surface, in which the plasticizer resistanceand water resistance can be increased without curing the primer layer.

Accordingly, the present invention provides a primer compositioncomprising a solvent and a polymer dispersed or dissolved in thesolvent, the composition being applicable to a surface to form a primerlayer when dried after the application, wherein the polymer ispolycarbonate polyurethane having a recurring unit derived frompolycarbonate polyol in the molecule.

In this primer composition, the solvent is preferably an aqueous solventcontaining water and the polycarbonate polyurethane is dispersed in theaqueous solvent.

The present invention further provides a bonded structure comprising (1)a base material, (2) a primer layer comprising a polymer adhered to thebase material, and (3) an adhesive sheet having an adhesive layeradhered to the primer layer, wherein the polymer is polycarbonatepolyurethane having a recurring unit derived from polycarbonate polyolin the molecule.

The base material preferably has a resin and a plasticized resin layercontaining the resin and a plasticizer for the resin, and the primerlayer adhered to the plasticized resin layer.

DETAILED DESCRIPTION OF THE INVENTION

The primer polymer in the primer composition of the present inventioncontains polycarbonate polyol polyurethane, enabling a primer layerformed from the primer composition to have increased plasticizerresistance and water resistance without curing.

From the viewpoint of environmental protection, it is preferable thatthe solvent used for the primer composition is an aqueous solvent.

The primer composition of the present invention is particularly usefulfor forming bonded structures that are used in places where water ispresent. Specifically, the bonded structure comprises (1) a basematerial, (2) a primer layer containing a polymer adhered to said basematerial, and (3) an adhesive sheet having an adhesive layer adhered tothe primer layer and is used in places where water is present.

The high hydrolysis resistance of the primer layer formed from theprimer composition of the present invention is derived from thepolycarbonate skeleton possessed by the polycarbonate polyolpolyurethane in the molecule. The bonded structure having such a primerlayer can effectively prevent the bonding strength (peeling resistance)between the base material and the adhesive sheet from decreasing, evenif it is used in places where water is present.

In addition, the polycarbonate polyol polyurethane has excellentplasticizer resistance. Therefore, the plasticizer is effectivelyprevented from moving from the base material to the adhesive layer of anadhesive sheet when the base material has a plasticized resin layer. Itis believed that such plasticizer resistance is based on thepolycarbonate skeleton and polyurethane bond possessed by thepolycarbonate polyol polyurethane, which results in high cohesion force.Such a cohesion force increases the intermolecular attractive forceamong polyurethane molecules, effectively preventing the plasticizerfrom immersing into the primer layer. Therefore, the bonded structurehaving such a primer layer effectively prevents the plasticizer frommigrating from the base material to the adhesive sheet, whereby adecrease in the cohesive force of the adhesive layer is effectivelyprevented.

In addition, the primer layer formed from the primer composition of thepresent invention does not require curing after forming by applying theprimer composition to obtain the above-described high performance.Therefore, if the primer composition contains substantially no curingagent, the process time can be shortened as compared to using a curedprimer that requires a period of time to cure the primer layer. Inaddition, the primer composition of the present invention does notrequire the weighing and blending procedures that are required fortwo-liquid type primer composition, making it easy to form the bondedstructure. Furthermore, the primer composition can be easily stored fora long period of time.

Primer Composition

The primer composition is a coating composition comprising a solvent anda polymer (primer polymer) dispersed or dissolved in the solvent. Thiscoating composition forms a coating film where applied and dried. Theprimer polymer contains a polycarbonate polyurethane. When the solventis an organic solvent, the primer polymer is usually dissolved in thesolvent. When the solvent is an aqueous solvent, the primer polymer isusually dissolved in the solvent.

Methyl ethyl ketone, toluene, and ethyl acetate, for example, can beused as the organic solvent. Examples of the aqueous solvent includewater and a mixture of water and alcohol. As examples of alcohol,alkylene glycol mono-alkyl ether esters such as dipropylene glycolmonomethyl ether and 3-methyl-3-methoxybutyl acetate can be given.Aqueous primer compositions exhibit a smaller impact on environment.Therefore, an aqueous primer substantially consisting of water is idealin view of ecology.

The nonvolatile component concentration of the primer composition isusually 5–50 mass %, preferably 10–40 mass %, and particularlypreferably 15–30 mass %. If the nonvolatile component concentration istoo small, it is difficult to form a coating (a primer layer) with asufficient thickness and the drying speed may be retarded. In addition,when the surface to be coated is a vertically elongated object (withrespect to the ground), the coated primer composition may run down thesurface. On the contrary, if the nonvolatile component concentration istoo high, application operation itself may be difficult or it may bedifficult to produce a coating with a flat surface. If the coatingsurface is not flat and smooth, the bonded structure formed by applyingan adhesive sheet on the coating may have impaired appearance.

The composition is usually coated using a brush, spray, roller, or thelike. The primer layer is typically dried at a temperature of 10–120° C.for 1 minute to 10 hours. When the primer composition contains anaqueous medium, for example, the primer layer may be formed by drying ina room environment (usually 25° C., 65% RH) for 0.5–2 hours. The drythickness of the primer layer is usually 1–200 μm, and preferably 2–100μm.

The content of the primer polymer in the primer layer formed from theprimer composition in the total primer layer is usually 70 mass % ormore, preferably 80 mass % or more, and particularly preferably 90 mass% or more. If the content of the primer polymer is too small, ordinarybonding strength (peeling resistance of the adhesive sheet adhered tothe primer layer), water resistance, and plasticizer resistance may beimpaired.

The primer polymer may contain a polymer other than polycarbonatepolyurethane. Such a polymer may be polystyrene, styrene-butadienecopolymer, polyamide, acrylic resin, polyurethane (polyetherpolyurethane and polycaprolactone polyurethane) other than thepolycarbonate polyurethane, and the like. The content of the primerpolymer in the primer layer formed from the primer composition in thetotal primer layer is usually 60 mass % or more, preferably 70 mass % ormore, and particularly preferably 80 mass % or more. If the content ofthe polycarbonate polyurethane is too small, the water resistance andplasticizer resistance may be impaired.

Additives other than the primer polymers may be added to the primercomposition insofar as the effect of the present invention is notadversely affected. Such additives may include a repellency preventiveagent, thickener, anti-foaming agent, leveling agent, UV absorber,antioxidant, and the like. An additive such as a surfactant and the likehaving a hydrophilic functional group in the molecule may move to thesurface of the primer layer (the adhering surface with the adheringsheet), resulting in a decrease in the water resistance of the primerlayer. Therefore, it is desirable to limit the content of such asurfactant or use with a high molecular weight exhibiting low surfacemigration characteristics. The number average molecular weight of thesurfactant is preferably 1,000–30,000. When a surfactant having a numberaverage molecular weight of less than 1,000 is used, the amount shouldbe preferable 5 mass % or less, and particularly preferably 3 mass % orless of the total mass of the primer layer.

The repellency preventive agent prevents the primer composition frombeing repelled when applied to the base material surface or the like andeasily increases surface smoothness of the primer layer formed from adry coating of the composition. In the case of an aqueous primercomposition, a repellency preventive agent dispersible or soluble in anaqueous medium is preferably added. The repellency preventive agent is apolymer having a number average molecular weight usually of1,000–30,000. The polymer has a hydrophobic main chain and side chainscontaining hydrophilic functional groups. Examples include water solublepolymers (or oligomers), water dispersible polymers (or oligomers), andhigh molecular weight surface active agents.

Examples of the main chain for such a compound with a comparatively highmolecular weight include polyurethanes, acrylic polymers, and silicones.Typical acrylic polymers are acrylic acid ester copolymer of alcoholhaving 6 or less carbon atoms, polyacrylic acid, and ammonia-modifiedpolyacrylic acid. The acrylic acid ester copolymer is a copolymer madefrom starting monomers containing an acrylic ester of alcohol having 6or less carbon atoms and a monomer having a hydroxyl group in themolecule. The polyacrylic acid is usually a polymer containing acrylicacid and acrylic ester as starting monomers. The amount of therepellency preventive agent is usually 0.1–7 mass %, and preferably0.2–5 mass % for 100 mass % of the primer polymer.

The primer composition can be prepared by mixing the above raw materialsusing a high speed mixer or homogenizer and homogeneously dissolving ordispersing the primers and other components. The viscosity of the primercomposition determined by a Brookfield type viscometer is generally50–800 mPa·s, preferably 70–500 mPa·s, and more preferably 80–300 mPa·s.If the viscosity is too low, the composition may run down the coatedsheet making it difficult to produce a uniform coating. On the otherhand, if the viscosity is too high, the coating operation may bedifficult.

Although there are no specific limitations, the glass transitiontemperature (Tg) of the primer layer is usually 20–50° C. Tg in thepresent invention is determined from Tan δ which is measured using adynamic viscoelasticity measurement apparatus under the conditions of atwist mode of shear rate=1 radian/sec, a temperature range of −60° C. to100° C., and a rate of temperature rise of 5° C./sec. The thickness ofsamples was usually 1–2 mm.

Polycarbonate Polyurethane

Polycarbonate polyurethane is a polyurethane having a repeating unitderived from polycarbonate polyol in the molecule. Preferably, thepolycarbonate polyurethane is a polymer obtained by polymerizing rawmaterials containing a polycarbonate polyol and a diisocyanate. A shortchain diol such as neopentyl glycol, ethylene glycol, or propyleneglycol may be added to the raw materials as a chain extender.

IPDI (isophorone diisocyanate), MDI (diphenylmethane diisocyanate),hydrogenated MDI; 1,6-hexanediol diisocyanate, TDI (tolylenediisocyanate), TMXDI (tetramethylxylylene diisocyanate), and the likemay be used as the diisocyanate. The raw material may contain one ormore polycarbonate polyols and one or more diisocyanates.

The alkylene carbon atom number of the polycarbonate polyol ispreferably 4–8, and particularly preferably 5–7. If the carbon atomnumber is too large, the plasticizer resistance of the primer layertends to decrease; if too small, on the other hand, the water resistanceof the primer layer may decrease. The weight average molecular weight ofthe polyurethane is usually 20,000–1,000,000, but is not limited to thisrange.

When an aqueous solvent is used for the primer composition, thepolyurethane is preferably a self-emulsification type polymer having anionic hydrophilic functional group in the molecule. Such a polyurethanecan homogeneously disperse in the solvent without using a surfactant,whereby the decrease in water resistance due to oozing of the surfactanton the surface of the primer layer can be effectively prevented.

The ionic functional group in the self-emulsification type polymer ispreferably one or more groups selected from the group consisting of asulfonate, carboxylate, phosphoric acid, betaine, sulfobetaine,sulfonium salt (e.g. —S⁺R₂.X⁻, wherein R is a methyl or hydrogen and Xis a halogen ion), phosphonium salt (—P⁺R₃.X⁻, wherein R is a methyl orhydrogen and X is a halogen ion), and nitrogen-containing cationicfunctional group. The nitrogen-containing cationic functional group isone or more groups selected from the group consisting of an amine salt,quaternary ammonium salt (e.g. —N⁺R₃.X³¹ , wherein R is methyl orhydrogen and X is a halogen ion), pyridinium salt (e.g. —N⁺C₅H₅.X⁻,wherein X is a halogen ion), and polyethylene polyamine (e.g.—NH(C₂H₄NH)_(m)H, wherein m is 2–4).

The self-emulsification type polyurethane usable in the presentinvention can be prepared in accordance with a conventional method ofpolyurethane synthesis. For example, such a polyurethane can be preparedby reacting polyisocyanate with a polyol mixture containing an ionicpolyol having an ionic functional group and polycarbonate polyol.Another method is to directly incorporate a unit having an ionicfunctional group in the molecule of polycarbonate polyol.

The ionic polyol can be synthesized from aromatic dicarboxylic acidcontaining a sulfonate in the molecule (e.g. dimethyl sodiumsulfoisophthalic acid) or aromatic dicarboxylic acid diester (e.g.dimethyl sodium sulfoisophthalate), for example. When the functionalgroup is a quaternary ammonium group, polyurethane can be prepared byreacting (1) a mixture of a compound having an active hydrogen atom anda tertiary amino group in the molecule and a polyol and (2) apolyisocyanate to obtain a precursor polymer, then quaternarizing thetertiary amino group.

Bonded Structure

A bonded structure with excellent water resistance and plasticizerresistance can be obtained in the present invention by forming a primerlayer on the surface of a base material using the above primercomposition. Specifically, the bonded structure comprises (1) a badematerial, (2) a primer layer containing the polycarbonate polyurethanesticking fast to said base material, and (3) an adhesive sheet having anadhesive layer stuck fast to said primer layer. Since the primer layerof the present invention exhibits superior plasticizer resistance, theprimer layer is particularly useful in a bonded structure comprising aresin and a plasticized resin layer containing the resin and aplasticizer. In this instance, the primer layer is stuck fast to theplasticized resin layer.

A base material having a plasticization resin layer has beenconventionally used as an interior decorative board. Such a conventionalinterior decorative board includes a base material having a plasticizedresin layer as an outermost surface layer and a base material made froma resin containing a plasticizer. As examples of the interior decorativeboard, a PVC coated steel plate and a decorative board with the surfacecoated with an adhesive sheet containing a supporting body having aplasticized resin layer can be given. The PVC coated steel plateconsists of a steel plate and a plasticized vinyl chloride resin layercovering the surface of the steel plate. The plasticizer is usually aplasticizer for polyvinyl chloride such as DOP (dioctyl phthalate). Thistype of decorative board is used for forming walls or floors in roomswhere water is used such as a bathroom, kitchen, lavatory, and indoorpool. The primer layer of the present invention is used for adhering anadhesive sheet to the surface of the plasticizer resin layer of thedecorative board.

An adhesive sheet conventionally used for interior finish work such asan ornamental sheet and decorative sheet can be used. Such a sheet has asupporting member and an adhesive layer secured to the supportingmember, and is caused to adhere to the primer layer via the adhesivelayer. A resin film containing a highly pliable resin is preferably usedfor the supporting member. Specifically, resins such as polyvinylchloride resin, fluorine-containing resin, phthalate polyester (PET,PEN, etc.), acrylic resin, and polyolefin resin are used as the resinfilm material. Although there are no specific limitations to thethickness of the supporting member, the thickness is usually from about10 to 800 μm. The supporting member may contain two or more layersinasmuch as the required pliability is not impaired. In addition, ametal foil such as an aluminum foil may be included to the extent thatthe pliability is not impaired.

Although not specifically limited, the adhesive layer of the adhesivesheet usually contains an acrylic polymer. Since the acrylic polymerpossesses high hydrolysis resistance, this material is suitable for useby adhering to walls and the like of rooms where water is used. On theother hand, the acrylic adhesive layer has low plasticizer resistance.The primer layer of the present invention, therefore, can supplement theweak point of the acrylic adhesive layer and effectively prevent thedecrease in the adhesive force due to a plasticizer and water, therebyincreasing reliability of the bond structure.

The acrylic polymer contains a self-adherent polymer, for example.Preferably, the acrylic polymer contains an acrylic self-adherentpolymer and a crosslinking agent which can crosslink the polymer. Theself-adherent polymer is herein defined as a polymer exhibitingtackiness at an ordinary temperature (about 25° C.).

One example of the self-adherent acrylic polymer will now be described.First, an acrylic unsaturated acid (such as acrylic acid, methacrylicacid, itaconic acid, or maleic acid) or a polar (meth)acrylic monomersuch as acrylonitrile is used as a first monomer. Then, a monomermixture of the first monomer and an acrylic monomer, as a secondmonomer, is prepared. As the second monomer, an alkyl acrylate such asiso-octyl acrylate, butyl acrylate, 2-methylbutyl acrylate, 2-ethylhexylacrylate, or isononyl acrylate can be used. The monomer mixture issynthesized into the self-adherent polymer with a prescribed molecularweight by a conventional polymerization method such as solutionpolymerization, emulsion polymerization, or mass polymerization.

The amount of the crosslinking agent for crosslinking the self-adherentpolymer varies according to the type of the self-adherent polymer, butis usually 0.02–2 mass %, and preferably 0.03–1 mass % for 100 mass % ofthe self-adherent polymer. As the crosslinking agent, an isocyanatecompound, melamine compound, poly(meth)acrylate compound, epoxycompound, amide compound, and bisamide compound such as a bisaziridinederivative of a dibasic acid (e.g. isophthaloylbis(2-methylaziridine canbe used.

The glass transition temperature (Tg) of the adhesive layer is usuallyfrom −50° C. to 0° C., and preferably from −45° C. to −5° C. Tg of theadhesive layer is determined from Tan □ which is measured using adynamic viscoelasticity measurement apparatus under the conditions of atwist mode of share rate=1 radian/sec, a temperature range of −60° C. to100° C., and a rate of temperature rise of 5°/sec. The thickness ofsamples was usually 1–2 mm.

The thickness of the adhesive layer is usually 20–100 μm, and preferably25–80 μm. The adhesive layer may contain additives such as a tackifier,minute elastic balls, minute tacky polymer balls, crystal polymers,inorganic powder, and UV absorbers insofar as the effect of the presentinvention is not impaired.

EXAMPLES

The present invention is described below in more detail by examples.However, the present invention is not limited the following examples.

Example 1

0.25 mass % of a repellency preventive agent (D-38, nonvolatilecomponent concentration: 52%, manufactured by Dainichiseika Color &Chemicals Mfg. Co., Ltd.) was added to 100 mass % of aself-emulsification type water dispersible polycarbonate urethane resinsolution (D6260, manufactured by Dainichiseika Color & Chemicals Mfg.Co., Ltd.). The mixture was homogeneously blended to obtain a primercomposition of the present invention. The nonvolatile componentconcentration of the polycarbonate urethane resin solution was 20 mass%. The repellency preventive agent was a water soluble acrylicacid/n-butyl copolymer having hydroxyl groups in the molecule. Thenumber average molecular weight of the copolymer (determined by GPC,styrene-reduced) was 2,100.

The primer composition was applied to the surface of a plasticized vinylchloride resin layer of a PVC coated steel plate (“Hishimetal”manufactured by Mitsubishi Plastics Industries Ltd.) using a brush andallowed to stand for one hour in a room at about 25° C. and 65% RH toobtain a primer layer stuck fast to the vinyl chloride resin layer. Thethickness of the primer layer was 6.5 μm. The vinyl chloride resin layercontained DOP as a plasticizer.

An adhesive sheet (an ornamental film “DI-NOC Film” manufactured by 3MCorp.) was adhered to the primer layer on the PVC coated steel andpressed with a 2 kg hand roller to form a bond structure of the presentinvention. The ornamental film had a supporting member of a vinylchloride resin sheet and an adhesive layer containing acrylic tackypolymer secured on the back of the supporting member, with a plandimension of 150 mm×25 mm.

The primer layer thus formed had a flat and smooth surface. Noirregularities impairing the appearance were observed on the surface ofthe ornamental sheet adhered on the primer layer. The same polycarbonateurethane resin solution not containing the repellency preventive agentwas applied to the surface of the PVC coated steel plate. The coatedsolution was repelled and a flat and smooth primer layer could not beformed.

Example 2

A primer layer was prepared in the same manner as in Example 1 exceptfor using the polycarbonate urethane resin solution with a nonvolatilecomponent concentration of 15 mass %. The bonded structure was preparedusing this primer layer in the same manner as in Example 1. Thethickness of the primer layer was 5 μm.

Comparative Example 1

A bonded structure was prepared in the same manner as in Example 1except that the primer layer was not formed.

Comparative Example 2

A bonded structure was prepared in the same manner as in Example 1except that a primer composition (“WP-3000” manufactured by 3M Company)containing an acrylic polymer as a primer polymer was used. This primercomposition contained water as a solvent.

Comparative Example 3

A bonded structure was prepared in the same manner as in Example 1except that a primer composition (“WP-2000” manufactured by 3M Company)containing chloroprene rubber as a primer polymer was used. This primercomposition contained water as a solvent.

Comparative Example 4

A bonded structure was prepared in the same manner as in Example 1except that a primer composition containing polyester polyurethane as aprimer polymer was used.

Evaluation of Bonded Structures

The bonded structures obtained in the above examples were evaluated asfollows. The evaluation results are shown in Table 1.

-   (1) Adhesive Force Under Ordinary Conditions

Bonded structures allowed to stand for two days in a room at about 25°C. and 65% RH after completion were used as samples. The adhesive forceunder ordinary conditions was determined by measuring peel strength whenthe samples were peeled at an angle of 180° at a drawing speed of 300mm/min.

-   (2) Adhesive Force Under Heating

Bonded structures allowed to stand still for seven days in an oven at65° C. after completion were used as samples. The adhesive force underheating was determined by measuring peel strength when the samples werepeeled at an angle of 180° at a drawing speed of 300 mm/min.

-   (3) Water Resistance of Adhesive Force

The bonded structures were dipped in water at 40° C. for seven days. Thewater resistance of adhesive force was determined by measuring peelstrength when the samples were peeled at an angle of 180° at a drawingspeed of 300 mm/min.

TABLE 1 Comparative Example Example 1 2 1 2 3 4 Adhesive force underordinary 21 21 22 22 35 21 conditions (N/25 mm) Adhesive force underheating 20 19 12 8 11 20 (N/25 mm) Water resistance of adhesive 22 19 195 11 5 force (N/25 mm)

The plasticizer resistance of the primer layer can be evaluated from theresults of the adhesive force in Table 1. Specifically, samplesexhibiting almost no decrease in the adhesive force after heating arejudged to possess excellent plasticizer resistance. In the evaluation ofthe water resistance of adhesive force, not only water but alsosurfactants in the primer layer are suspected to have affected theresults. A surfactant with a comparatively low molecular weight wasincluded in the primer compositions in Comparative Examples 2 and 3.Oozing of the surfactant on the surface from the inside of the primerlayer is considered to be one reason for the decrease in the waterresistance of adhesive force.

As described above, the plasticizer resistance and water resistance ofthe primer composition and bonded structure of the present invention canbe effectively increased even if the primer layer is not cured.

1. A bonded structure comprising: (1) a base material comprising aplasticizing resin layer containing a resin and a plasticizer for theresin, (2) a primer layer containing a polymer sticking fast to saidplasticizing resin layer, the polymer contaning a polycarbonatepolyurethane having a repeating unit derived from polycarbonate polyolin a molecule thereof, and (3) an adhesive sheet having an adhesivelayer stuck fast to said primer layer; wherein the primer layereffectively prevents the plasticizer from migrating from the basematerial to the adhesive sheet.
 2. The bonded structure of claim 1,wherein the primer layer exhibits plasticizer resistance without beingcured.
 3. The bonded structure of claim 1, wherein the primer layercomprises at least 70 mass percent polymer.
 4. The bonded structure ofclaim 1, wherein the primer layer comprises at least 80 mass percentpolymer.
 5. The bonded structure of claim 1, wherein the adhesive layercomprises an acrylic polymer having low plasticizer resistance, and theprimer layer prevents plasticizers present in the plasticizing resinlayer from reaching the adhesive layer.
 6. A bonded structurecomprising: (1) a base material comprising a plasticizing resin layercontaining a resin and a plasticizer for the resin, (2) a primer layercontaining a polymer sticking fast to said plasticizing resin layer, thepolymer containing a polycarbonate polyurethane having a repealing unitderived from polycarbonate polyol in a molecule thereof, wherein theprimer layer has a thickness of 1 to 200 micrometers, and (3) anadhesive sheet having an adhesive layer stuck fast to said primer layer.7. The bonded structure of claim 6, wherein the primer layer has athickness of 2 to 100 micrometers.
 8. The bonded structure of claim 6,wherein the adhesive layer has a thickness of 20 to 100 micrometers. 9.The bonded structure of claim 6, wherein the adhesive layer has athickness of 25 to 80 micrometers.
 10. A bonded structure comprising:(1) a base material comprising a plasticizing resin layer containing aresin and a plasticizer for the resin, (2) a primer layer containing apolymer sticking fast to said plasticizing resin layer, the polymercontaining a polycarbonate polyurethane having a repeating unit derivedfrom polycarbonate polyol in a molecule thereof, and (3) an adhesivesheet having an adhesive layer stuck fast to said primer layer, whereinthe adhesive layer has a thickness of 20 to 100 micrometers.
 11. Thebonded structure of claim 10, wherein the adhesive layer has a thicknessof 25 to 80 micrometers.
 12. The bonded structure of claim 10, whereinthe primer layer has a thickness of 1 to 200 micrometers.
 13. The bondedstructure of claim 10, wherein the primer layer has a thickness of 2 to100 micrometers.
 14. The bonded structure of claim 1, wherein theadhesive sheet further comprises a support member.
 15. The bondedstructure of claim 14, wherein the support member is a resin film. 16.The bonded structure of claim 14, wherein the support member is fromabout 10 to 800 micrometers thick.